Pupils at three south Wales secondary schools have had their bags checked by sniffer dogs to highlight how police can trace drugs.
Toby the sniffer dog was brought in to test the pupils' bags
Gwent Police were invited into Croesyceiliog, Llantarnam and Fairwater schools by teachers as a drugs education initiative.
Police said they were not looking to prosecute if drugs had been discovered. As it turned out, none were found.
Officers told pupils it was not a "drugs bust" but a demonstration.
The three schools agreed to let police take in sniffer dog Toby, who examined the students' bags.
He was also sent into classrooms and officers also carried out swabs in classrooms to find traces of drugs.
Pc Darrel Dewar, who helped organise the exercise, said: "There is a problem in all schools with drugs.
"In the past we have dealt with drug dealers at the gates of schools and we want the young people to have informed choices.
"This isn't about hauling kids into the back of a van if we find anything, this is to show them just what we can do to detect substances."
The first demonstration was held at Croesyceiliog with pupils from year 11.
The students were invited into the school hall and asked to put their bags at the front before the police brought in the dog to examine the bags. No drugs were found, however.
Before the exercise was carried out, pupils were told any drugs found would be taken away and destroyed, and the matter would be left to the school to handle.
"We have very good relationship with the local schools. The head teachers of the schools wanted to raise awareness of the dangers and consequences of drug use," said Pc Dewar.
The demonstration was watched by the pupils
"Even if the drug is not on the child, or in their bag, there are ways and means of detecting whether they have come into contact with the smallest traces.
"We are hopeful that if the youngsters know there is a possibility they could be caught and punished if they have come into contact with drugs, this will be a deterrent for them," he added.
School head Helene Mansfield said: "This was to make sure that the pupils have facts not fiction to make choices in the future.
"We have had some substance abuse education in the school and this demonstration was to show what the police can do.
"I'm not naive enough to say that none of our pupils dabble in drugs - that would be stupid. I'm sure many do and so had there been a positive result I would not have been surprised.
"But nor am I surprised that nothing has been found."
She said had any of the pupils been caught with drugs, their parents would have been informed.
"I think is has been very useful for the students to see what can be done and in a fairly low-key sort of way."
The police were unable to find drugs in any of the bags of pupils checked in all three schools.